Fiberglass insulation products consist of glass fibers bonded together with covalently crosslinked binder resins. Processes for making fiberglass insulation generally include drawing molten streams of glass to spinning wheels where they are spun into thin fibers by centrifugal forces. The fibers are then blown into a forming chamber, sprayed with an aqueous binder and deposited as a mat onto a traveling conveyor. Thereafter, the coated mat is transferred to a curing oven where heated air is blown through the mat to cure the binder and rigidly bond the glass fibers together.
Fiberglass binders used in the present sense should not be confused with matrix resins which are an entirely different and non-analogous field of art. While sometimes termed “binders,” matrix resins act to fill the entire interstitial space between fibers, resulting in a dense, fiber reinforced product where the matrix must translate the fiber strength properties to the composite, whereas “binder resins” as used herein are not space-filling, but rather coat only the fibers, and particularly the junctions of fibers. Fiberglass binders also cannot be equated with paper or wood product “binders” where the adhesive properties are tailored to the chemical nature of the cellulosic substrates. Many such resins, e.g. urea/formaldehyde and resorcinol/formaldehyde resins, are not suitable for use as fiberglass binders. One skilled in the art of fiberglass binders would not look to cellulosic binders to solve any of the known problems associated with fiberglass binders.
Binders useful in fiberglass insulation products generally require a low viscosity in the uncured state, and yet have the characteristic ability to form a rigid thermoset polymeric mat with the glass fibers when cured. A low binder viscosity in the uncured state allows the mat to be sized correctly. Also, viscous binders tend to be tacky or sticky and hence they lead to accumulation of fiber on the forming chamber walls. This accumulated fiber may later fall onto the mat causing dense areas and product problems. A binder which forms a rigid matrix when cured is desired so that a finished fiberglass thermal insulation product, when compressed for packaging and shipping, will recover to its specified vertical dimension when installed in a building.
Phenol-formaldehyde (PF) resins, as well as PF resins extended with urea, are widely used throughout the fiberglass insulation industry. Such resins are inexpensive, have low viscosity, and cure to form a rigid polymer, thereby providing the finished product with excellent physical properties.
A serious disadvantage of PF resins is the high concentration of free formaldehyde, which is normally partially scavenged with urea. During the curing reaction, formaldehyde and low molecular weight phenol-formaldehyde compounds are volatilized from the binder into the surrounding environment. Therefore, there is a continuing need for alternative fiberglass binder that would not emit formaldehyde upon curing.
A number of formaldehyde-free compositions have been developed for use as a binder for making fiberglass insulation products.
U.S. Pat. No. 4,076,917 discloses the use of beta-hydroxyalkylamides to cure polycarboxy polymers such as polyacrylic acid. Such a system, however, is too viscous for use as a binder for glass fibers.
U.S. Pat. Nos. 6,221,973 and 6,331,350 describe a formaldehyde-free fiberglass binder including a polyacid, such as polyacrylic acid, and a polyol, with a molecular weight less than about 1000, such as, for example, glycerol, triethanolamine, sorbitol, or ethylene glycol. A phosphorous catalyst is used to accelerate the cure of the composition.
U.S. Pat. No. 5,932,689 describes a curable aqueous composition for fiberglass insulation, which contains (a) a polyacid comprising at least two carboxylic acid groups, anhydride groups, or salts thereof; (b) an active hydrogen-containing compound, such as polyol or polyamine, and (c) a cyanamide, a dicyanamide or a cyanoguanidine. Suitable accelerators include phosphorous or fluoroborate salts.
WO 03/104284 describes an epoxide-type formaldehyde-free insulation binder containing a substantially infinitely water-dilutable or water-dispersable mixture of an epoxide and a multi-functional cross-linker, such as polyamidoamine polymer.
U.S. Pat. No. 5,006,140 discloses the use application of a water dispersion of a gelatinized starch sulphamate as a binder for glass wool. Such dispersions have the disadvantage that it is more difficult to spray them onto the fiber. The viscosity of the gelatinized starch is too high, so when used on wool, the composition has poor flowability. Also, the starch binder in the composition is merely gelated and does not chemically bond as a crosslinker to the resin.
Despite these disclosures, there is a growing need for new formaldehyde-free aqueous compositions suitable for use as a binder for fiberglass insulation. Some of the drawbacks and limitations of disclosed systems include high cost, high viscosity, low pH causing corrosion of metal parts of the production lines, and high cure temperature. Moreover, because fossil resources will be scarce in the future, there will be an increased need for binders made out of renewable resources. Thus, new formaldehyde-free binders having lower cost and using renewable materials would be desirable.